Coordinate measuring apparatuses are commonly used in many industries to analyze the contour of a workpiece or to verify manufacturing compliance with specifications. In a first type of apparatus, a probe is mounted on an articulated, multi-axis measurement arm. The probe is manually brought in contact with a point on a workpiece to verify its Cartesian coordinates. The probe can also be dragged along a contoured surface in order to determine its spherical or cylindrical coordinates. Digital encoders installed within each articulation of the arm generate orientation signals that are fed to a data processor which extracts from those signals the desired coordinate values. An example of this first type of coordinate measuring apparatus is disclosed in my U.S. Pat. No. 5,829,148 incorporated herein by this reference.
In a second type of coordinate measuring apparatus, the probe mounted on a multi-axis adjustable support is automatically driven into contact with the workpiece by computer-controlled motors which directs the movement of various structural elements of the apparatus that are orthogonally oriented in reference to one another. Optical or tactile sensors mounted within the probe stop the movement of the pillars or arms when contact with the workpiece is established. An example of this second type of coordinate measuring apparatus is disclosed in U.S. Pat. No. 5,134,782 incorporated herein by this reference.
Due to the multiple components, particularly moving parts, present in the first type of coordinate measuring machine, high precision is seldom achieved. This type machine is also particularly sensitive to temperature variations. The second type of coordinate measuring machine tend to be sturdier, have a limited number of coordinate-transferring parts and, accordingly, can provide higher precision. However, they are also bulkier, heavier and more complex.
The instant invention results from an attempt to devise a lightweight, yet precise coordinate measuring device which can be adapted to operate as a robotic tool by taking advantage of new material having improved capabilities.